"999 is enough for anybody" triple-zero padding (#18)

When I hit 999 exercises, I will finally have reached the ultimate
state of soteriological release and no more exercises will be needed.
The cycle will be complete. All that will be left is perfect quietude,
freedom, and highest happiness.

exercises/031_switch2.zig

@@ -0,0 +1,42 @@
+//
+// What's really nice is that you can use a switch statement as an
+// expression to return a value.
+//
+//     var a = switch (x) {
+//         1 => 9,
+//         2 => 16,
+//         3 => 7,
+//         ...
+//     }
+//
+const std = @import("std");
+
+pub fn main() void {
+    const lang_chars = [_]u8{ 26, 9, 7, 42 };
+
+    for (lang_chars) |c| {
+        var real_char: u8 = switch (c) {
+            1 => 'A',
+            2 => 'B',
+            3 => 'C',
+            4 => 'D',
+            5 => 'E',
+            6 => 'F',
+            7 => 'G',
+            8 => 'H',
+            9 => 'I',
+            10 => 'J',
+            // ...
+            25 => 'Y',
+            26 => 'Z',
+            // As in the last exercise, please add the "else" clause
+            // and this time, have it return an exclamation mark "!".
+        };
+
+        std.debug.print("{c}", .{real_char});
+        // Note: "{c}" forces print() to display the value as a character.
+        // Can you guess what happens if you remove the "c"? Try it!
+    }
+
+    std.debug.print("\n", .{});
+}